Refresh rate for HTPC with Projector

[ilkand]

Do all projectors have a 60hz refresh rate for their native resolution? Are there any with a 75hz refresh, for example? And where can I find details, please? If not, is 60hz a problem when playing (panning) a PAL dvd? My collection is mainly PAL.

Thanks
Andy

[Gary Lightfoot]

Not all projectors are locked at 60 hz, and not all have problems with PAL sources.

My previous pj the Davis DLS8 would sync to any frequency you gave it, so running at 72hz for NTSC and 75hz for PAL was the best solution.

I now have an NEC HT1000 which runs at 50hz or 60hz as far as I can tell, but doesn't seem to have any problems with 60hz for PAL which seems strange. I guess that it detects the PAL source and works out the frame rate from there. It even works OK with 72 and 75hz.

I believe all LCDs are locked though, but I'm not definite about that. Hopefully more people will chime in with more info for you.

Gary.

[Gordon @ Convergent AV]

I know it's the wrong forum but CRT's don't care as long as you are within bandwidth limitations.....

Also 75 and 72 can actually result in more obvious judder. Now, if you could do 25 or 24 Hz that might be interesting...who knows....might do it at Event2......................................NOT promising anything.

Gordon

Gordon

[Gary Lightfoot]

You're such a tease sometimes Gordon.

You've piqued my curiosity - what causes the judder you mention with 72/75hz?

Cheers.

Gary.

[Gordon @ Convergent AV]

Well it's actually a pshycological phenomenon. I've had a few beers but I'll try to explain.


Basically your brain is quite smart. It can recognise refresh rates. It sees 48Hz refresh and sees 48 FRAMES. The problem is it sees those 48 frames but only sees movement in 24 of them.....

Imagine a ball is kicked across a field. 24 pictures are taken. Our brain sees 1/48TH of a second the ball in Position 1. nEXT 48TH it's STILL in position 1. The next 48TH it's in Position 2. Next 48TH it's in position 2 STILL but our brains are going....hang on it should have moved further. Now if you are doing 72 Hz refresh you can get same issues in that your brain expects to see position of ball further along course of travel but it hasn't moved. Flicker may have reduced but that is only an issue with phosphor based devices. ....

I don't know whether we can do it yet but I'd like to see what folk thought of 24Hz V 60Hz with a suitable display

Jeez it's late.....zzzzzzzzzzzzzzzzzzzzzzzz

G

[Gary Lightfoot]

Basically your brain is quite smart. It can recognise refresh rates. It sees 48Hz refresh and sees 48 FRAMES. The problem is it sees those 48 frames but only sees movement in 24 of them.....

Thanks Gordon, nice explanation.

So would you say this is generaly something that not everybody sees? I can't say that I've ever noticed it, but then again, I don't see DLP rainbows either.

Guess I'm pretty lucky considering I have a DLP and an HTPC.

Gary.

[ilkand]

I knew that about CRTS (been reading up ), but every time I see an expensive and huge CRT that I'd be interested in, the people on the CRT forum suggest running it at 800x600, which doesn't seem much. I have an HTPC (PDI / x-card combo)which i got because it was supposed to improve on juddery pans, but surely won't if you do PAL at 60hz.

All confused now

[Gordon @ Convergent AV]

I know it's a nightmare......

Garry, I honestly don't know. This is all theory to me until tested.
AND even then as you have pointed out what we all perceive may not be the same

Ilkland: Yes doing 50 to 60 frame rate conversion is goin gto add judder but this may result in a less objectionable image in other respects......nothing is simple

Gordon